@Argamis  
that’s some great theory… and yet sadly it makes earthponies even worse :/

@Sandblast  

 
Near the end of the season 8 finale [FiM_S8E26].

@Argamis  
Which episode is that?

@Argamis  
Pinkie’s magic doesn’t enter through her forehead, it actually goes to her face, between her eyes and sort of on her snout. Apparently Pinkie Pie’s face is where her magic is located?

Actually sounds pretty good in English too. Kimiko Glenn is a great singer. :D

0:19 - I can’t! Sunny is soooo cute here :)

@Sandblast  

 
This is actually canon.  
-> When the Arcana Magic returned to all magical creatures of Equestria (including unicorns & alicorns), a purple/red glow of magic went inside the upper side of her forehead (at the same time a purple/violet one went into Twilight).
 
An actual unicorn with an incomplete/damaged horn (Tempest Shadow) is still able to project her magic (in chaotic, potentially destructive ways); so perhaps an under_developed one may simply “warp reality” around the pony.

This is how a unicorn struts  
Watch you shake your unicorn butt  
Now you’re in the unicorn know  
Soon you’ll be a unicorn pro
 
Oh, a unicorn horn makes a unicorn stride  
It’s the warhead on your forehead, it’s the source of your pride  
Every unicorn who’s born is borne a horn that’s unique  
So I’ll whip them up if you seek, you be lookin’ très magnifique!
 
This is how a unicorn walks  
This is how a unicorn talks  
Now you’re looking unicorn gold  
This is how a unicorn ends its song

@Sunsetbrony55
 
Pinkie Pie was a unicorn with an inner horn.

yup she kinda reminds me of pinkie pie